In motor-vehicles the internal combustion engine drives an auxiliary device, such as an electric power generator. A connecting gear unit is operatively interconnected between the internal combustion engine and auxiliary device. This connecting gear unit has a changeable transmission ratio. By change of the transmission ratio the r.p.m. of the auxiliary device can be approximated to a desired r.p.m. in spite of large variations of the r.p.m. of the internal combustion engine during operation.
The operation and control of the connecting gear unit requires a circuitry comprising electric and/or hydraulic and/or pneumatic circuit components. Frequently, it is desirable to provide at least part of such components outside of the connecting gear unit. If certain components are provided outside the gear unit, it is necessary to provide connecting means between internal components provided within the connecting gear unit and external components provided outside the gear unit. These connecting means should be arranged in such a way as to require a minimum of space in the engine compartment of e.g. a motor-vehicle. This requirement is particularly important as in many cases the speed change operations in the connecting gear unit are not only dependent on the r.p.m. of the respective engines but are additionally responsive to other parameters of the engine, the motor-vehicle, the driving conditions and the environmental conditions.